Light and Color

What is the relationship between light and color?

Electromagnetic Spectrum

Light is color. Light is defined as the part of the electromagnetic
spectrum that is visible to the human eye. The visible portion of the
spectrum covers a wave-length range from approximately 380 nm to 780
nm. The human eye regards the green/yellow portion as brighter and the
outer blue/red portion of the spectrum as darker. General purpose lamps
are designed to focus in the green/yellow portion of the spectrum to
provide brightness when lighting offices, schools, warehouses, etc.

Promolux lamps are designed to encompass a full portion
of the spectrum. Including the darker colors will give a slight impression
of less brightness, but it will dramatically increase the vividness of
colors that exist in the merchandise placed beneath the lamps.

How is true color measured?

Many of the present methods of measuring the quality of a light source
in terms of its color rendering are outdated, misleading and inadequate
for today's technology. i Despite this understanding among all lighting
technology experts, the light suppliers continue to define the quality
of a light source by the "Color Rendering Index" (CRI) and its "Kelvin
Correlated Color Temperature" (CCT).

Methods which use criteria such as "Color Preference Index" (CPI), "Color
Definition Index" (CDI), "Color Saturation", "Color Gamut" and other
parameters such as UV and Infrared content are becoming widely used by
leading lighting scientists. ii These methods which will soon define
quality lighting, use sophisticated software and computers that measure
light based on the human eye perception of color.

As it is already documented in numerous publications, so we will only
point out a few of the problems related to CCT and CRI. The Kelvin CCT
was designed to compare the chromacity of incandescent lamps. It is still
valid for that use, but it is quite inadequate to compare fluorescent
tubes of different "Spectral Power Distribution" (SPD). For example,
it is possible to have two very different fluorescent lamps in color
such as green and pink, yet both having the same CCT.

An incandescent lamp by definition has a CRI of nearly 100. This however
does not mean that the incandescent bulb has an ideal color rendering.
It can easily be seen that an incandescent bulb distorts all colors with
an excessive yellow glow with too little blue content.

It is also defined
that outdoor daylight has a CRI of 100. However, we all know that a north
sky light distorts colors due to its high blue and very low red content.
Furthermore, all daylight is not the same and its chromacity changes
depending on the region, various seasons or even the hours of the day.
Yet by "definition" they are all natural daylight with a CRI of 100.

The CRI was designed to compare lighting sources of similar and continuos
SPD with the same chromacity. These factors must be considered when making
lamp comparisons, otherwise visual distortions result such as lamps with
a lower CRI showing a much better color rendering while another lamp
with a higher CRI will provide poor color rendering.